From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
To: "Wang, Yipeng1" <yipeng1.wang@intel.com>,
"Richardson, Bruce" <bruce.richardson@intel.com>,
"De Lara Guarch, Pablo" <pablo.de.lara.guarch@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
"Gavin Hu (Arm Technology China)" <Gavin.Hu@arm.com>,
Steve Capper <Steve.Capper@arm.com>,
Ola Liljedahl <Ola.Liljedahl@arm.com>, nd <nd@arm.com>,
"Gobriel, Sameh" <sameh.gobriel@intel.com>
Subject: Re: [dpdk-dev] [PATCH 4/4] hash: enable lock-free reader-writer concurrency
Date: Mon, 1 Oct 2018 04:11:28 +0000 [thread overview]
Message-ID: <AM6PR08MB3672857E5877EF22794E8DB198EF0@AM6PR08MB3672.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <D2C4A16CA39F7F4E8E384D204491D7A6614D8226@FMSMSX151.amr.corp.intel.com>
> >
> >Add the flag to enable reader-writer concurrency during run time. The
> >rte_hash_del_xxx APIs do not free the keystore element when this flag
> >is enabled. Hence a new API, rte_hash_free_key_with_position, to free
> >the key store element is added.
> >
> >+/** Flag to support lock free reader writer concurrency */ #define
> >+RTE_HASH_EXTRA_FLAGS_RW_CONCURRENCY_LF 0x08
> [Wang, Yipeng] It would be good to indicate that the lockless implementation
> works for single writer multiple readers.
Multi-writers are supported by using the rw-lock or transactional memory. Essentially, we still have single writer. This patch works fine with multi-writer as defined by ' MULTI_WRITER_ADD' flag. I have tested it as well. I will enable this test case in V2.
> Also, if people use a mix of the flags for example set both multiwriter and LF
> flags, then I guess either we need to return an error or maybe multiwriter
> should have higher priority. Currently the RW_CONCURRENCY will assume
> MULTI_WRITER_ADD I think.
As mentioned above, multi-writer and LF combination is supported. Yes, RW_CONCURRENCY currently assumes MULTI_WRITER_ADD. I think we should separate them.
> >+
> > /** Signature of key that is stored internally. */ typedef uint32_t
> > hash_sig_t;
> >
> >@@ -143,6 +148,11 @@ rte_hash_count(const struct rte_hash *h);
> > * and should only be called from one thread by default.
> > * Thread safety can be enabled by setting flag during
> > * table creation.
> >+ * When lock free reader writer concurrency is enabled,
> >+ * if this API is called to update an existing entry,
> >+ * the application should free any memory allocated for
> >+ * previous 'data' only after all the readers have stopped
> >+ * using previous 'data'.
> [Wang, Yipeng] Could you be more specific on this description?
> When add_key API is called, the users do not know if it will update an existing
> entry or inserting a new one, do they?
I think, it will depend on the application. The applications I have worked on so far, added a hash entry as a result of receiving an event and updated it on receiving another event. I can change the comments to indicate that the applications need to be aware of add/update operations.
>
> > *
> > * @param h
> > * Hash table to add the key to.
> >@@ -165,6 +175,11 @@ rte_hash_add_key_data(struct rte_hash *h, const
> >void *key, void *data);
> > * and should only be called from one thread by default.
> > * Thread safety can be enabled by setting flag during
> > * table creation.
> >+ * When lock free reader writer concurrency is enabled,
> >+ * if this API is called to update an existing entry,
> >+ * the application should free any memory allocated for
> >+ * previous 'data' only after all the readers have stopped
> >+ * using previous 'data'.
> > *
> > * @param h
> > * Hash table to add the key to.
> >@@ -230,6 +245,12 @@ rte_hash_add_key_with_hash(struct rte_hash *h,
> >const void *key, hash_sig_t sig);
> > * and should only be called from one thread by default.
> > * Thread safety can be enabled by setting flag during
> > * table creation.
> >+ * If lock free reader writer concurrency is enabled,
> >+ * the hash library's internal memory for the deleted
> >+ * key is not freed. It should be freed by calling
> >+ * rte_hash_free_key_with_position API after all
> >+ * the readers have stopped using the hash entry
> >+ * corresponding to this key.
> > *
> > * @param h
> > * Hash table to remove the key from.
> >@@ -241,6 +262,8 @@ rte_hash_add_key_with_hash(struct rte_hash *h,
> const void *key, hash_sig_t sig);
> > * - A positive value that can be used by the caller as an offset into an
> > * array of user data. This value is unique for this key, and is the same
> > * value that was returned when the key was added.
> >+ * When lock free concurrency is enabled, this value should be used
> >+ * while calling the rte_hash_free_key_with_position API.
> > */
> > int32_t
> > rte_hash_del_key(const struct rte_hash *h, const void *key); @@ -251,6
> >+274,12 @@ rte_hash_del_key(const struct rte_hash *h, const void *key);
> > * and should only be called from one thread by default.
> > * Thread safety can be enabled by setting flag during
> > * table creation.
> >+ * If lock free reader writer concurrency is enabled,
> >+ * the hash library's internal memory for the deleted
> >+ * key is not freed. It should be freed by calling
> >+ * rte_hash_free_key_with_position API after all
> >+ * the readers have stopped using the hash entry
> >+ * corresponding to this key.
> > *
> > * @param h
> > * Hash table to remove the key from.
> >@@ -264,6 +293,8 @@ rte_hash_del_key(const struct rte_hash *h, const
> void *key);
> > * - A positive value that can be used by the caller as an offset into an
> > * array of user data. This value is unique for this key, and is the same
> > * value that was returned when the key was added.
> >+ * When lock free concurrency is enabled, this value should be used
> >+ * while calling the rte_hash_free_key_with_position API.
> > */
> > int32_t
> > rte_hash_del_key_with_hash(const struct rte_hash *h, const void *key,
> >hash_sig_t sig); @@ -290,6 +321,30 @@
> rte_hash_get_key_with_position(const struct rte_hash *h, const int32_t
> position,
> > void **key);
> >
> [Wang, Yipeng] If possible, how about having a new delete function instead of
> modifying the current one?
> I think it does not need to be tied with the lockless implementation, it is
> orthogonal to multi-threading implementation.
> people using locks may still want this new deletion behavior.
> If people want old behavior, they can call current API, otherwise they can call
> the new deletion function, followed by Rte_hash_free_key_with_position later.
I like the terms 'delete' and 'free'. I am finding it hard to come up with a good name for the API. It will be on the lines of 'rte_hash_del_key_with_hash_no_free' - I do not like the name much.
Instead, we could have a configuration flag for the hash table, 'RTE_HASH_EXTRA_FLAGS_FREE_MEM_ON_DEL'. If this is enabled, 'rte_hash_del_...' APIs will free the key store index and any internal memory. Enabling lock-free RW concurrency will enable this flag. User can enable this flag explicitly while not using lock-free RW concurrency as well.
next prev parent reply other threads:[~2018-10-01 4:11 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-06 17:12 [dpdk-dev] [PATCH 0/4] Address reader-writer concurrency in rte_hash Honnappa Nagarahalli
2018-09-06 17:12 ` [dpdk-dev] [PATCH 1/4] hash: correct key store element alignment Honnappa Nagarahalli
2018-09-27 23:58 ` Wang, Yipeng1
2018-09-06 17:12 ` [dpdk-dev] [PATCH 2/4] hash: add memory ordering to avoid race conditions Honnappa Nagarahalli
2018-09-28 0:43 ` Wang, Yipeng1
2018-09-30 22:20 ` Honnappa Nagarahalli
2018-10-01 22:41 ` Wang, Yipeng1
2018-10-01 10:42 ` Ola Liljedahl
2018-10-02 1:52 ` Wang, Yipeng1
2018-09-06 17:12 ` [dpdk-dev] [PATCH 3/4] hash: fix rw concurrency while moving keys Honnappa Nagarahalli
2018-09-28 1:00 ` Wang, Yipeng1
2018-09-28 8:26 ` Bruce Richardson
2018-09-28 8:55 ` Van Haaren, Harry
2018-09-30 22:33 ` Honnappa Nagarahalli
2018-10-02 13:17 ` Van Haaren, Harry
2018-10-02 23:58 ` Wang, Yipeng1
2018-10-03 17:32 ` Honnappa Nagarahalli
2018-10-03 17:56 ` Wang, Yipeng1
2018-10-03 23:05 ` Ola Liljedahl
2018-10-04 3:32 ` Honnappa Nagarahalli
2018-10-04 3:54 ` Honnappa Nagarahalli
2018-10-04 19:16 ` Wang, Yipeng1
2018-09-30 23:05 ` Honnappa Nagarahalli
2018-10-01 22:56 ` Wang, Yipeng1
2018-10-03 0:16 ` Wang, Yipeng1
2018-10-03 17:39 ` Honnappa Nagarahalli
2018-09-06 17:12 ` [dpdk-dev] [PATCH 4/4] hash: enable lock-free reader-writer concurrency Honnappa Nagarahalli
2018-09-28 1:33 ` Wang, Yipeng1
2018-10-01 4:11 ` Honnappa Nagarahalli [this message]
2018-10-01 23:54 ` Wang, Yipeng1
2018-10-11 5:24 ` Honnappa Nagarahalli
2018-09-14 21:18 ` [dpdk-dev] [PATCH 0/4] Address reader-writer concurrency in rte_hash Honnappa Nagarahalli
2018-09-26 14:36 ` Honnappa Nagarahalli
2018-09-27 23:45 ` Wang, Yipeng1
2018-09-28 21:11 ` Honnappa Nagarahalli
2018-10-02 0:30 ` Wang, Yipeng1
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